The visual approach slope indicator (VASI) is a system of
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
s on the side of an airport
runway
According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt concrete, as ...
threshold that provides visual
descent
Descent may refer to:
As a noun Genealogy and inheritance
* Common descent, concept in evolutionary biology
* Kinship, one of the major concepts of cultural anthropology
**Pedigree chart or family tree
** Ancestry
** Lineal descendant
**Heritag ...
guidance information during approach. These lights may be visible from up to during the day and up to or more at night.
Basic visual approach slope indicators consist of one set of lights set up some from the start of the runway. Each light is designed so that it appears as either white or red, depending on the angle at which it is viewed. When the pilot is approaching the lights at the proper angle, meaning the pilot is on the
glide slope
Instrument landing system glide path, commonly referred to as a glide path (G/P) or glide slope (G/S), is "a system of vertical guidance embodied in the instrument landing system which indicates the vertical deviation of the aircraft from its o ...
, the first set of lights appears white and the second set appears red. When both sets appear white, the aircraft is too high, and when both appear red it is too low. This used to be the most common type of visual approach slope indicator system; however, it is being phased out and replaced by
precision approach path indicator
A precision approach path indicator (PAPI) is a visual aid that provides guidance information to help a pilot to acquire and maintain the correct approach (in the vertical plane) to an airport or an aerodrome. It is generally located on the left- ...
s (PAPIs), which are closer together and therefore more efficient to sight and maintain.
A mnemonic to remember the colors and their meaning is:
: White over White, you're high as a kite / you'll fly all night / check your height / you're out of sight
: Red over White, you're alright.
: Red over Red, you're dead.
: White over Red, unsaid / you're under head / you land on your head.
("White over red" isn't actually possible unless the VASI installation is badly off, the white and red filtered glasses on the lights were fitted upside down by accident, or else if the pilot is accidentally flying upside-down on final.)
Pulsating VASI
The pulsating visual approach slope indicator (PVASI) is a system similar in purpose to a VASI, but only consists of one piece of equipment. It indicates the pilots height on approach with a mix of red and white, steady and pulsating light. Pulsating white light indicates that the aircraft is too high, whereas steady white indicates being on glide path. Steady red light is meant to show a position only slightly below glide path, with pulsating red light being indicative of a position well below glide path. This type of system is less prevalent than other visual glide slope indicators like regular VASIs or PAPIs, as of May 2022 there were only 84 PVASIs installed at 51 airports and heliports in the United States and its territories according to
Federal Aviation Administration
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
data, compared to 6730 PAPIs and 623 VASIs.
[{{Cite web , title=Airport Data and Information Portal , url=https://adip.faa.gov/agis/public/#/public , access-date=2022-05-09 , website=adip.faa.gov , publisher=]Federal Aviation Administration
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
See also
*
Leading lights
Leading lights (also known as range lights in the United States) are a pair of light beacons used in navigation to indicate a safe passage for vessels entering a shallow or dangerous channel; they may also be used for position fixing. At night ...
, similar aid to navigation
*
Pilot controlled lighting Pilot-controlled lighting (PCL), also known as aircraft radio control of aerodrome lighting (ARCAL) or pilot-activated lighting (PAL), is a system that allows aircraft pilots to control the lighting of an airport or airfield's approach lights, run ...
(PCL)
*
Precision approach path indicator
A precision approach path indicator (PAPI) is a visual aid that provides guidance information to help a pilot to acquire and maintain the correct approach (in the vertical plane) to an airport or an aerodrome. It is generally located on the left- ...
(PAPI)
*
Runway end identifier lights
Runway end identifier lights (REIL) (ICAO identifies these as Runway Threshold Identification Lights) are installed at many airports to provide rapid and positive identification of the approach end of a particular runway. The system consists of a ...
(REIL)
*
Runway edge lights
Runway edge lighting are used to outline the edges of runways during periods of darkness or restricted visibility conditions. These light systems are classified according to the intensity they are capable of producing:
* High intensity runway l ...
(HIRL, MIRL, LIRL)
*
Approach lighting system
An approach lighting system (ALS) is a lighting system installed on the approach end of an airport runway and consisting of a series of lightbars, strobe lights, or a combination of the two that extends outward from the runway end. ALS usually ...
(ALS)
*
Optical landing system
An optical landing system (OLS) (nicknamed "meatball" or simply "ball") is used to give glidepath information to pilots in the terminal phase of landing on an aircraft carrier.
From the beginning of aircraft landing on ships in the 1920s to the i ...
References
FAA Aeronautical Information Manual, Chapter 2 (Aeronautical Lighting and Other Airport Visual Aids), Section 1 (Airport Lighting Aids)
External links
FAA Aeronautical Information Manual
Airport lighting
Optical communications
fr:Vasi